Skype

Skype differs from other major VoIP players insofar as it is designed more on the lines of an IM service that offers voice communication rather than a program designed to completely mimic traditional telephony. This means that it runs on a platform that allows for instant messaging, a convenient tool for those that want to send files across the internet while they are speaking. The service also comes with a host of other supported features like 3 and 4 way calling, call-waiting, voicemail, and customizable ringtones.

But while all of these features are added bonuses, the real standout feature of Skype is that it is free.